The integration degree of integrated circuits is recently more and more increasing and in the production of a semiconductor substrate of VLSI (i.e., i.e., ultra-LSL) or the like, an ultrafine pattern comprising lines having a width of half-micron or less must be processed. For satisfying this requirement, the wavelength used by an exposure apparatus for use in lithography is more and more shifted to a shorter wave and at present, studies are being made on the use of excimer laser light (e.g., XeCl, KrF, ArF) at a shorter wavelength out of far ultraviolet rays.
For the pattern formation of lithography in this wavelength region, a chemical amplification-type resist is used.
The chemical amplification-type resist in general can be roughly classified into three groups commonly called 2-component system, 2.5-component system and 3-component system. The 2-component system uses a combination of a compound capable of generating an acid upon photochemical decomposition (hereinafter referred to as a “photo-acid generator”) and a binder resin. This binder resin is a resin having in its molecule a group capable of decomposing under the action of an acid and thereby increasing the solubility of the resin in an alkali developer (sometimes referred to as an “acid decomposable group”). The 2.5-component system further contains a low molecular compound having an acid decomposable group in addition to the 2-component system. The 3-component system contains a photo-acid generator, an alkali-soluble resin and the above-described low molecular compound.
This chemical amplification-type resist is suitable as a photoresist for the irradiation with ultraviolet ray or far ultraviolet ray but must further respond to the required properties on use.
With respect to the photoresist composition for ArF light source, a resin where an alicyclic hydrocarbon site is introduced for the purpose of imparting dry etching resistance has been proposed. However, the introduction of alicyclic hydrocarbon site incurs a problem, that is, the system becomes very hydrophobic, as a result, the development with an aqueous tetramethylammonium hydroxide (hereinafter referred to as “TMAH”) solution which has been heretofore widely used as a resist developer cannot be performed or there occurs a phenomenon such that the resist falls off from the substrate during the development.
To cope with this hydrophobitization of resist, an organic solvent such as isopropyl alcohol is mixed in the developer and there is provided an effect, however, the problem is not completely solved because the resist film may swell or the process becomes cumbersome. From the standpoint of improving the resist, a large number of techniques have been proposed to compensate for various hydrophobic alicyclic hydrocarbon sites by the introduction of a hydrophilic group.
JP-A-9-73173 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes a resist material using an acid-responsive compound containing a structure unit which contains an alkali-soluble group protected by an alicyclic group-containing structure and renders the compound alkali-soluble upon elimination of the alkali-soluble group under the action of an acid.
JP-A-11-119434 describes a resist material using a resin containing a repeating unit having an alicyclic hydrocarbon and a repeating unit having a lactone structure, which is an inexpensive resist material having high resolution and high sensitivity and improved in the dry etching resistance.
However, in the micro-photofabrication using far ultraviolet ray, particularly, ArF excimer laser ray, these conventional positive resist compositions fail in providing good results in view of sensitivity, defocus latitude depended on line pitch or surface roughening at the etching.